Field of the Invention
The invention relates to a control for a motor vehicle drive having an automatic transmission, including an engine control with which a variable that influences the torque of the engine is controlled, and a transmission control with which shifting events of the transmission are controlled and with which an intervention signal for initiating a shifting event is transmitted to the engine control.
Such a control for a motor vehicle drive with an automatic transmission must control the transmission in such a way that shifting proceeds comfortably and in particular without jerking or jolting. Wear of the friction elements, namely clutches and brakes, in the transmission should also be kept as low as possible. To that end, slipping or scraping times must not exceed a predetermined duration. For that purpose, an intervention into the engine control is made during shifting, in order to vary and in most cases reduce the torque.
The engine control in a control system known from German Patent DE 29 35 916 C2, corresponding to U.S. Pat. No. 4,403,527, includes a plurality of performance graphs, and the intervention signal forwarded from the transmission control to the engine control is merely a switchover signal, by means of which a shift from a first to a second performance graph is made. The second performance graph effects reduced values for the engine torque for various operating states of the engine, for instance in order to damp the increase in moment from the engagement of a free-running clutch in the automatic transmission and thus to reduce the jerking upon shifting or the wear of slipping or scraping friction elements in the transmission. The reduced engine torque values must be ascertained by the transmission manufacturer through costly experimentation. Other variables influencing the reduction of engine torque cannot be taken into account.
It is accordingly an object of the invention to provide a control for a motor vehicle drive having an automatic transmission, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, which enables comfortable and low-wear shifting and which takes other variables influencing the shifting process into account.